A flash of light that streaked across the sky over the east coast of the United States was probably a single meteor, Nasa has announced.

"Judging from the brightness, we're dealing with something as bright as the full moon," said Bill Cooke, who works for Nasa's Meteoroid Environmental Office.

"We basically had a boulder enter the atmosphere over the northeast."

Mr Cooke said the meteor had been widely seen, with hundreds of reports on social media like Twitter as well as the website of the American Meteor Society.

Society official Robert Lunsford said it "basically looked like a super bright shooting star".

The flash in the sky was spotted as far south as Florida and as far north as New England.

Eyewitness Matt Moore said he had been standing in line for a concert in Philadelphia around dusk when he saw a "brilliant flash moving across the sky at a very brisk pace ... and utterly silent".

"It was clearly high up in the atmosphere," he said. "But from the way it appeared, it looked like a plane preparing to land at the airport."

Mr Moore said the flash was visible to him for about two or three seconds, and then it was gone. He described it as having a "spherical shape and yellowish and you could tell it was burning, with the trail that it left behind".

Derrick Pitts, the chief astronomer at Philadelphia's Franklin Institute, agreed that the sightings had all the hallmarks of a "fireball".

Mr Pitts said this one got more attention because it happened on a Friday evening - and because Twitter had provided a way for people to share information on the sighting.

He said what people probably saw was one meteor - or a "space rock" - that may have been the size of a volleyball falling fairly far down into the Earth's atmosphere.

He likened it to a stone skipping across the water - getting a "nice long burn out of it."

Mr Pitts said experts could not be 100% certain of what it was, unless it actually fell to the ground and they could track its trajectory.

But he said the descriptions by so many people were "absolutely consistent" with those of a meteor.